Fabrication of can bodies with integral bottom walls

ABSTRACT

TO PRODUCE A CYLINDRICAL CAN BODY, A SHEET METAL BLANK OF AN INITIAL THICKNESS SUBSTANTIALLY GREATER THAN THE DESIRED WALL THICKNESS OF THE CAN BODY IS POSITIONED WITH A CENTRAL PORTION OF THE BLANK BETWEEN TWO COOPERATING DIES OF SUBSTANTIALLY THE DIAMETER DESIRED FOR THE CAN BODY AND THE TWO DIES COMPRESS THE CENTRAL PORTION OF THE SHEET METAL BLANK ACROSS ITS THICKNESS TO THIN THE CENTRAL PORTION OF THE BLANK BY RADIAL EXTRUSION OF SURPLUS METAL. THE CONSEQUENT RADIAL DISPLACEMENT OF METAL DISTORTS THE BLANK TO AN INTERMEDIATE CONFIGURATION OF A RECEPTTACLE HAVING A CONICAL CIRCUMFERENTIAL WALL WITH THE AXIAL DIMENSION OF THE RECEPTACLE SUBSTANTIALLY SHORT OF THE AXIAL DIMENSION DESIRED FOR THE FINISHED CAN BODY. THE RECEPTACLE IS PLACED ON A MANDREL THAT CONFORMS TO THE INSIDE DIMENSIONS OF THE DESIRED CAN BODY FOR THE PURPOSE OF CARRYING OUT A SPINNING OPERATION THAT NOT ONLY THINS THE CIRCUMFERENTIAL WALL OF THE RECEPTACLE AND SHAPES THE   CIRCUMFERENTIAL WALL TO THE CYLINDRICAL CONFIGURATION OF THE MANDREL BUT ALSO INCREASES THE AXIAL DIMENSION. THIS SPINNING OPERATION IS CARRIED OUT BY ROLLING MEANS, SUCH AS BALL MEANS, WHICH IS MOVED HELICALLY AROUND THE MANDREL.

March 23, 1971 c, ZE 3,572,271

FABRICATION OF CAN BODIES WITH INTEGRAL BOTTOM WALLS Filed May 23, 1968 4 Sheets-Sheet 1 Er/rra/ C. Fry n:

March 23, 1971 E. c. FRAZE 3,572,271

FABRICATION OF CAN BODIES WITH INTEGRAL BOTTOM WALLS Filed May 23. 1968 4 Sheets-Sheet 2 March 23, 1971 FRAZE 3,572,271

FABRICATION OF CAN BODIES WITH INTEGRAL BOTTOM WALLS Filed May 23,- 1968 4 Sheets-Sheet 3 March 23, 1971 E. C. FRAZE FABRICATION OF CAN BODIES WITH INTEGRAL BOTTOM WALLS Filed May 23, 1968 4 Sheets-Sheet 4 zdz/ vg 4270016)? United States Patent 3,572,271 FABRICATION OF CAN BODIES WITH INTEGRAL BOTTOM WALLS Ermal C. Fraze, Dayton, Ohio, assignor to Dayton Reliable Tool & Mfg. Company, Dayton, Ohio Filed May 23, 1968, Ser. No. 731,592 Int. Cl. BZld 51/00 US. Cl. 113-120 11 Claims ABSTRACT OF THE DISCLOSURE To produce a cylindrical can body, a sheet metal blank of an initial thickness substantially greater than the desired wall thickness of the can body is positioned with a central portion of the blank between two cooperating dies of substantially the diameter desired for the can body and the two dies compress the central portion of the sheet metal blank across its thickness to thin the central portion of the blank by radial extrusion of surplus metal. The consequent radial displacement of metal distorts the blank to an intermediate configuration of a receptacle having a conical circumferential wall with the axial dimension of the receptacle substantially short of the axial dimension desired for the finished can body. The receptacle is placed on a mandrel that conforms to the inside dimensions of the desired can body for the purpose of carrying out a spinning operation that not only thins the circumferential wall of the receptacle and shapes the circumferential wall to the cylindrical configuration of the mandrel but also increases the axial dimension. This spinning operation is carried out by rolling means, such as ball means, which is moved helically around, the mandrel.

BACKGROUND OF THE INVENTION Various fabrication procedures have been employed heretofore for the production of cans of the general type commonly used for beverages and food products. In the fabrication of a tin coated steel can, a cylindrical shell is first formed out of sheet metal and then a stamped sheet metal bottom is assembled to one end of the shell.

To avoid the necessity of separately fabricating a single shell and a bottom wall, it is highly desirable to form a can body with an integral bottom wall and such onepiece can bodies made of aluminum alloy have been produced heretofore.

One prior art method of producing a one-piece aluminum can body is to use progressive drawing dies to produce an aluminum body of somewhat less than the desired axial dimension and then to place the body on a mandrel for the purpose of ironing the cylindrical wall of the body by means of a hard metal or carbide ring to thin the metal and to elongate the cylindrical wall to the desired axial dimension.

Another prior art method of producing a one-piece aluminum can body employs impact extrusion to produce an intermediate cup-shaped workpiece. It is not practical to extrude such an intermediate workpiece in a single impact stroke because it would be too severe on the dies and because slight defects in the metal and the presence of minute bodies of lubricant would result in too many rejects, and therefore repeated extrusion is employed. The product of the repeated extrusion is placed on a mandrel and is finished to the desired final dimension by using a hard metal ring for a simple ironing operation.

Unfortunately, an ironing operation produces rejects if the metal is scratched or if a foreign particle gets in the way. A further disadvantage, moreover, is that if the ironing ring is not floatingly supported with a certain freedom for lateral movement, the metal may pile up at one point of the ring to result in rupture of the workpiece and, on the other hand, if the ironing ring is floatingly supported, localized resistance, for example a local thick spot in the metal causes the mandrel and/ or ring to shift laterally to result in a nonuniform cylindrical wall.

All of these prior art techniques result in a can body in which the thickness of the metal is greater than necessary in some parts of the can and there is a pressing need for a method of fabricating a one-piece can body with greater economy of material. This need may be appreciated by setting forth ideal dimensions for a onepiece can body made of an aluminum alloy.

It has been found that the bottom Wall of an aluminum alloy can may be relatively thin and yet be of adequate strength by a liberal margin if the bottom wall is shaped to nonplanar configuration, for example, an inwardly bulged configuration. Thus an aluminum alloy can body of a common size of 2 ,4 inside diameter may have a bottom wall thickness of approximately .0125". It is further possible to make the cylindrical wall of a can relatively thin in the intermediate region between the ends of the can without reducing the strength of the can below a safe margin. Thus the cylindrical wall of 'an aluminum alloy can may abruptly taper in thickness from approximately .0125 near its bottom end to a minimum thickness of .006-.0065. It has also been found that if theupper open end of such an aluminum alloy can body is necked down to reduce diameter to permit the use of a top wall of reduced diameter, the necking down locally reinforces the cylindrical wall to permit the local thickness of the cylindrical wall to be reduced. Thus with the open end of the aluminum can body strengthened in this manner, the thickness of the cylindrical wall may be of a thickness of only .0060-.0065 throughout the major portion of its length with a thickness of approximately .0125 near the bottom end and a thickness of .0090-.O095" near the open end.

If an aluminum alloy can body were fabricated with the above specified thickness dimensions at the bottom wall and along the length of the cylindrical wall only twentyeight to thirty pounds of metal would be required to produce 1,000 can bodies with integral bottom walls. Unfortunately, however, neither progressive drawing alone, nor progressively drawing combined with an ironing operation is inherently capable of producing such an ideally dimensioning aluminum alloy can body. The aluminum alloy required in each instance is approximately thirty-eight to forty pounds for 1,000 can bodies with integral bottom walls. Theoretically, then, it is posible to save from eight to twelve pounds of aluminum alloy per thousand can bodies which means a saving in metal of 20 to 30%.

The economic significance of this fact may be appreciated when it is considered that with aluminum alloy can bodies produced by automatic machinery at rates as high as 600-700 cans per minute, of the cost of the cans is in the aluminum alloy, only 20% of the cost being labor, overhead and profit. Thus 20 to 30% saving in the amount of aluminum alloy that is required means a saving of 16 to 24% of the total cost for the can bodies. At the high rate of production made posible by automatic machinery, a saving of only 5% would pile up rapidly and the possibility of obtaining such a saving by some new fabrication technique would warrant investment of a large sum in a development program.

The present invention is directed to the problem of providing a fabrication technique for producing onepiece can bodies of desirable thickness dimensions. The thickness dimensions specified above for aluminum alloy are by way of example only, it being understood that a a other thickness dimensions would be specified for other metals such as steel and for other material such as ductile plastics.

SUMMARY OF THE INVENTION By way of example, the invention is described herein as applied to the production of aluminum alloy can bodies. The fabrication of a can body starts with a fiat aluminum alloy sheet blank having an initial thickness substantially in excess of the maximum thickness desired at any part of the wall of a finished can body. For example, to produce an aluminum alloy can body with an inside diameter of 2 an axial dimension of approximately 4%" with a maximum wall thickness of .0125" at the lower end of the can body, the thickness of the sheet metal blank may be .020.O25".

The first step is to form the sheet metal blank to an intermediate configuration of a receptacle having a conical circumferential wall, the bottom wall of the receptacle being of the desired diameter of 2 and the metal of the bottom wall being reduced to the desired thickness of approximately .0125". This first step is carried out by employing a pair of cooperating dies of substantially 2 diameter to squeeze a central portion of the blank with consequent thinning of the central portion of the blank by the cooperating dies and the consequent radial extrusion of the surplus metal converts the sheet metal blank into the desired intermediate configuration of a receptacle with a conical circumferential Wall. In the preferred practice of the invention the mating faces of the two dies are shaped to form circular strengthening ribs in the bottom wall of the receptacle.

The second step is to place the receptacle on a mandrel that is dimensined in accord with the desired inside dimensions of the can body and then to carry out a spinning operation for the purpose of reshaping the conical wall to the cylindrical configuration of the mandrel and for the further purpose of thinning the metal to extend the circumferential wall to the desired axial dimension required for the finished can body.

This spinning operation is carried out by applying rolling means to the circumferential wall of the receptacle beginning adjacent the bottom wall of the receptacle and moving the rolling means relative to the mandrel helically around the mandrel at an appropriate speed, say at 100200 rpm. to shape the metal to the configuration of the circumferential surface of the mandrel and to spread the metal longitudinally of the mandrel. An important advantage of such a spinning operation is that it actually heals defects in the metal such as cracks. The rolling means may be ball means or may be in the form of roller means with a narrow cylindrical surface and with a tapered nose adjacent one edge of the cylindrical surface. In the preferred practice of the invention, two pairs of diametrically opposite rolling elements are employed in a suitable holder with the four elements following four helical paths relative to the mandrel simultaneously and with the helical paths spaced close together to result in the desired smooth peripheral surface.

The spinning operation may be carried out in any suitable manner that provides for simultaneous relative rotation and relative axial movement between the mandrel and the holder for the four rolling elements. In this example of the spinning operation, the mandrel is rotated on its axis and simultaneously advanced axially.

A feature of the preferred practice of the invention is the concept of causing the paths of the four rolling elements to conform accurately to a cylindrical surface, i.e. to maintain the four rolling elements in a constant given radial distance from the axis of the mandrel and to employ a mandrel that varies in diameter along its length to cause the variations in thickness along the length of the cylindrical wall of the can body. For this purpose, the mandrel varies in diameter to cause the cylindrical wall of the can body to be of a thickness of approximately .0125 near the bottom wall of the 4 can body and to be of a thickness of approximately .O090-.0095" near the open end of the can body with the major portion of the length of the cylindrical wall of a thickness of approximately .0060.0065".

Thus the fabrication procedure results in a can body of the previously mentioned thickness dimension with consequent important savings in metal.

The features and advantages of the invention may be understood from the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, which are to be regarded as merely illustrative:

FIG. 1 is a longitudinal sectional view of a can body of the preferred configuration as produced by the invention;

FIG. 2 is a diagrammatic sectional view showing how a pair of dies may cooperate to form a flat sheet metal blank to an intermediate configuration of a receptacle hving a conical circumferential wall;

FIG. 3 is a diagrammatic sectional view indicating how the receptacle shown in FIG. 2 may be placed on a mandrel for a spinning operation by rolling means that thins and spreads the metal of the cylindrical wall of the receptacle to change the conical wall to a cylindrical wall of the desired extended axial dimension;

FIG. 3a is an end view of the mandrel shown in FIG. 3;

FIG. 4 is a transverse sectional view of a holder or cage confining four balls which may be employed for for the step of spinning the circumferential wall of the p;

FIG. 5 is a fragmentary section along the line 55 of FIG. 4;

FIG. 6 is a sectional view along the line 66 of FIG. 3 showing in plan view a stripper that may be employed with the mandrel on which the cup is processed;

FIG. 7 is a fragmentary sectional view along the line 77 of FIG. 6;

FIG. 8 is a view similar to FIG. 5 showing how a roller may be substituted for a ball;

FIG. 9 is a diagrammatic view showing the helical path of a ball along the cylindrical wall of the cup;

FIG. 10 is an enlargement of a portion of FIG. 9 in the area indicated by the circular arrow 10;

FIG. 11 is an enlarged section along the line 11--11 of FIG. 10 showing how the balls progressively displace metal of the cylindrical wall axially of the mandrel;

FIG. 12 is a view similar to FIG. 10 showing the path produced by the roller shown in FIG. 8; and

FIG. 13 is an enlarged cross section along the line 1313 of FIG. 12.

DESCRIPTION OF THE PREFERRED PRACTICE OF THE INVENTION FIG. 1 shows the preferred configuration of a can body that is the end result of the steps taught by the invention. It is to be noted that the can body is necked down to a reduced diameter near its open end to permit the can body to be closed by a can end of reduced diameter, this configuration strengthening the can body near its open end to permit the corresponding portion of the circumferential Wall of the can to be reduced in thickness.

It is contemplated that the can body shown in FIG. 1 will at least approximate most of the ideal thickness dimensions heretofore set forth. Thus the bottom wall of the can body may have thickness of approximately .0125"; the circumferential wall of the can body may be of the same thickness of .0125" near the bottom end and may be of a thickness of approximately .0O.0095 near the open end of the can body with a thickness of .0O60-.0065 along the major portion of the length of the cylindrical wall.

The fabrication of the can body begins with a flat circular sheet metal blank of thickness and a diameter to provide the volume of metal required for a can body.

The thickness of the sheet metal blank is substantially greater than is desired at any place in the wall of the finished can body. With the maximum thickness of the 'Wall of the can body shown in FIG. 1 approximately .0125", the thickness of the fiat sheet and metal blank may be .020-.025".

The first step of the process which is illustrated by FIG. 2 is to employ a pair of dies and 22 to squeeze the central area of the sheet metal blank to reduce the thickness of approximately .0125" with consequent radial extrusion of surplus metal. The radial extrusion forms a circumferential bead 24 of displaced metal and has the further effect of distorting the remainder of the sheet metal blank to conical configuration. Thus the result of this first die operation is a workpiece in the form of a receptacle 25 having a thin bottom wall 26 and a relatively thick conical circumferential wall 28.

Preferably the bottom wall 26 is shaped to nonplanar configuration for additional strength. In this instance the two dies 20 and 22 cooperate to form two circular ribs 30 and 32 in the bottom wall 26.

The next step which is illustrated by FIG. 3 is to telescope the receptacle 25 over a mandrel 34 which is dimensioned in accord with the inside dimensions of the final can body and which has an end wall 35 shaped to mate with the bottom ribs 30 and 32.

With the receptatcle telescoped over the mandrel 34, a spinning operation is carried out by applying rolling means under pressure to the circumferential Wall of the receptacle and rolling the rolling means in a helical path relative to the mandrel beginning in the region of the bottom of the receptacle thereby not only to spread and thin the metal of the conical Wall but also to shape the conical wall to the cylindrical configuration of the mandrel 34. This spinning operation is preferably carried out by a plurality of rolling means simultaneously with the rolling means equally spaced circumferentially of the mandrel to balance the forces across the mandrel. In this instance, four balls 36 are are used.

In the presently preferred practice of the invention, the spinning operation indicated in FIG. 3 is carried out by four balls 36 in a holder 40 that is constructed as indicated by FIGS. 3 and 4. The holder 40 has a thick cylindrical wall 44 and is formed with a wide inner circumferential groove 45 that houses four floating segments 46. Each of the four segments 46 is urged radially inwardly by a corresponding coil spring 47 that seats in a radial recess '48 the cylindrical -wall 44 and encloses a radial stem 50 of the corresponding segment. Each of the four balls 36 seats in a socket 52 of the corresponding segment 46 and protrudes through a circular aperture 54 of an inner cylindrical retaining member 56 that is secured to the segment, the circular aperture 54 being smaller than the diameter of the corresponding ball. Each segment 46 has a pair of parallel guide bores that slidingly receive corresponding guide pins 57 that are rnounted on the cylindrical wall 44. The four segments 46 mate at their radial faces 46a to limit the inward movement of the segments thereby to limit the inward movement of the balls 36 to insure that the helical paths of the inner surfaces of the four balls will conform to a cylindrical surface at a fixed radius from the axis of the mandrel 34. If desired, the four balls 36 may be hydraulically loaded instead of spring loaded.

It is contemplated that at the start of the spinning operation, the mandrel 34 will protrude above the surround structure by a dimension somewhat greater than initial axial dimension of the receptacle 25 and that the mandrel will be progressively advanced axially. It is further contemplated that a suitable stripper 58 will be mounted on the structure 60 that surrounds the mandrel 34, the purpose of the stripper being to engage the rim of the can body at the completion of the spinning operation. In the construction shown in FIGS. 3, 6 and 7 the inner circumference of the stripper 58 is formed with an 6 annular recess 62 to engage the rim of the can body at the end of the spinning operation. As shown in FIG. 6 the stripper 58 may be made in two halves which are provided with short parallel guide slots 64 in engagement with fixed limit pins 65, the two halves of the stripper being urged towards each other by suitable springs 66.

In the preferred practice of the invention, the stripping of the semi-finished can bodies from the mandrel 34 at the end of the spinning operation is facilitated by bursts of comprmsed air. For this purpose the mandrel 34 is provided with an axial air passage 68 which has a reduced end portion 69 at the end face of the mandrel. As shown in FIG. 3a the axial air passage communicates with a series of radial grooves 69a in the end surfaces of the mandrel to provide radial distribution of air. The compressed air in combination with the stripper 58 is highly effective to overcome the resistance to removal of the finished can body from the mandrel and with the bursts of air timed somewhat in advance of the mechanical stripping action, the mechanical stripping action does not deform the rim of the can body.

With the paths of the inner surfaces of the four balls 36 conforming accurately to a cylinder at a given radius from the axis of the mandrel 34, the thickness of the finished cylindrical wall of the can body may be varied along its length by varying the diameter of the mandrel 34 along its length. Therefore, the diameter of the mandrel will vary inversely with the desired thickness of the cylindrical wall of the finished can body. As heretofore stated and as indicated in FIG. 3, it is contemplated that the cylindrical wall of the finished can body will be approximately .0O60.0065" thick over the major portion of its length, with the thickness increased to approximately .0125 near the bottom end of the can body and increased to approximately .0090.0095 near the open end of the can body. Accordingly the mandrel is of greater diameter along the major potrion of its length than at its two ends. This bulging configuration of the mandrel increases the resistance to the tripping of the finished can body from the mandrel but the use of compressed air effectively overcomes this resistance.

The spinning operation is preferably carried out by rotating the mandrel 34 on its axis and simultaneously causing relative axial movement between the mandrel and the holder 40. For this purpose preferably the holder 40 is held stationary while the mandrel is simultaneously rotated and advanced axially.

With the four balls 36 of the stationary holder 40 in a common plane that is perpendicular to the axis of the mandrel, rotation of the mandrel without simultaneous axial advance of the mandrel would cause all four of the balls to follow the same circumferential path in the plane of the centers of the balls with no useful result. On the other hand, if the mandrel 34 is rotated relatively slowly on its axis and is simultaneously advanced axially at a relatively rapid rate, the four helical paths of the four balls would be spaced substantially and the balls would not cooperate on a common front of advancing metal. At the optimum ratio between the rate of rotation of the mandrel and the rate of axial advance of the mandrel, each ball 36 encroaches slightly on the slope of metal left by the preceding ball.

This action on the metal may be appreciated by reference to FIGS. 9 and 10 where the path of a single ball is indicated by a dotted helical line and a solid helical line 92 at uniform spacing from the dotted line. Above the dotted line 90 the circumferential Wall of the workpiece has been thinned uniformly to the desired thickness. The dotted line 90 represents the beginning of a slope formed by a ball. The thickess of the metal increases progressively in accord with the cross-sectional curvature of a ball 36 as may be seen in FIG. 11, the slope leading to a shoulder represented by the solid line 92 in FIG. 10, which shoulder is shown in section at 92 in FIG. 11 and is the leading shoulder of the progressively displaced metal.

7 In FIG. 11 the solid line curve 95 is the profile of a ball 36 that forms the slope and the dotted curve 96 is the profile of the next succeeding ball. It will be noted that the second ball is offset slightly from the first ball to cause a corresponding increment of advance of the slope to advance the leading shoulder 92 to the dotted position 92a. FIG. 8 indicates how each of the balls 36 may be replaced by a roller, generally designated 100, that has a narrow cylindrical surface 102 and a tapered nose 104. The roller 100 is mounted on an axle 105 that is pressed radially inwardly against retaining member 105. The axle 105 seats in a socket 108 of curved cross section in a segment 46a in a holder 40a of the character heretofore described. The segment 46a has a recess 109 to clear the roller and is urged radially outwardly in the previously described manner by a corresponding spring 47a.

FIGS. 12 and 13 correspond to FIGS. and 11 and show how the four rollers 100 cooperate to spin the circumferential wall of the workpiece on the mandrel 34. Here again a dotted line 110 represents the beginning of a conical slope that is formed by one of the rollers 100 and the solid line 112 represents the leading shoulder of the metal that is displaced by a roller, the shoulder being shown in section at 112 in FIG. 13. FIG. 13, shows in solid lines the profile of a roller 100 that forms the particular slope that is shown in cross section. The profile of the next succeeding roller is shown in dotted lines at 100a and it will be noted that the second roller 100a is slightly offset from the first roller to advance the leading shoulder of the displaced metal to the dotted position 112a.

The semi-finished can body that results from the spinning operation is trimmed to length, flanged at its rim and necked down in a well known manner to result in the final product shown in FIG. 1.

My description in specific detail of the presently preferred practice of the invention will suggest various changes, substitutions and other departures from my disclosure within the spirit and scope of the appended claims.

I claim: 1. A method of fabricating from ductile sheet material a cylindrical can body, characterized by the steps of:

providing a blank sheet of the ductile material of an initial thickness substantially greater than the desired thickness of the wall of the can body;

compressing across its thickness a central portion of the sheet blank of substantially the desired size of the bottom wall of the can body to reduce the thickness of said portion to the desired thickness of the bottom wall of the can body,

thereby squeezing the sheet material towards the periphery of the central portion with consequent thinning of the sheet material and radially outward displacement of excess metal,

thereby to distort the sheet blank into an intermediate configuration of a shallow receptacle with a conical circumferential wall of substantially less axial dimension than the desired axial dimension of the can body;

inserting into the receptacle a mandrel dimensioned in accord with the desired inner dimensions of the can body; and

increasing the axial dimension of the receptacle to at least the desired axial dimension of the can body by thinning the material of the circumferential wall of the receptacle against the periphery of the mandrel and spreading the material of the circumferential wall of the receptacle axially of the mandrel while shaping the circumferential wall of the receptacle to the configuration of the mandrel.

2. A method as set forth in claim 1 in which the compression of the central portion of the sheet blank across its thickness is carried out by cooperating dies shaped to convert said central portion to non-planar configuration for strengthening the bottom Wall of the can body.

3. A method as set forth in claim 2 in which said dies are shaped to form at least One circular offset rib in said portion of the blank sheet.

4. A method as set forth in claim 1 in which the thickness of the blank sheet is approximately twice the desired maximum thickness of the walls of the can body.

5. A method as set forth in claim 1 in which the step of increasing the axial dimension of the intermediate receptacle by thinning and spreading the material of the circumferential wall of the intermediate receptacle axially of the mandrel is carried out by applying rolling means to the circumferential Wall of the receptacle and rolling the rolling means along a helical path relative to the mandrel.

6. A method as set forth in claim 5 in which the helical path is substantially concentric to the axis of the mandrel and in which the mandrel tapers in diameter towards its opposite ends for maximum thinning of the material in the intermediate region of the length of the cylindrical wall of the finished can body.

7. A method of fabricating a cylindrical can body of ductile material, characterized by the steps of:

providing a blank sheet of the ductile material of an initial thickness substantially greater than the desired thickness of the circumferential wall and bottom wall of the can body;

forming the sheet blank to an intermediate configuration of a receptacle having a bottom wall of subtantially the size of the desired can body and having a conical circumferential wall of an axial dimension substantially less than the axial dimension of the can body and at the same time squeezing the material of the bottom wall to thin the bottom wall to substantially the desired thickness of the bottom wall of the can body and displacing surplus material of the bottom wall radially to the outer circumference of the receptacle;

inserting into the receptacle a mandrel dimensioned in accord with the desired inside dimensions of the can body; and

reshaping said conical wall to the configuration of the mandrel and at the same time displacing said radially displaced out material axially of the receptacle away from the bottom wall of the receptacle and displacing additional surplus material of the circumferential wall of the receptacle along the mandrel in the same direction to thin the cylindrical wall and to increase the axial dimension of the cylindrical wall to at least the desired axial dimension of the can body.

8. A method as set forth in claim 7 which includes distorting the bottom of the receptacle symmetrically to nonplanar configuration simultaneously with the step of thinnin g the bottom wall.

9. A method as set forth in claim 7 in which the reshaping of the outer circumferential wall of the receptacle and the displacing of surplus material to thin the outer circumferential wall is carried out by inserting into the receptacle a mandrel dimensioned in accord with the desired inside dimensions of the can body and the rolling means in a helical path relative to the mandrel about the mandrel beginning at the bottom end of the receptacle to progressively thin and spread the material of the circumferential wall of the receptacle longitudinally of the mandrel.

10. A method of fabricating a can body starting with a Work-in-process part of ductile material in the form of a receptacle having a bottom wall of substantially the desired diameter and thickness of the bottom wall of the can body and having a conical circumferential Wall of substantially greater thickness than the desired thickness of the circumferential wall of the can body and of substantially less than the desired axial dimension of the can body, said method including the steps of:

inserting into the receptacle substantially cylindrical mandrel of outside dimensions corresponding substantially to the desired inside dimensions of the can body; and

spacing rolling means from the periphery of the mandrel by a distance equal to the desired thickness of the circumferential wall of the can body and simultaneously causing relative movement between the rolling means and the mandrel axially of the mandrel and the rolling means about the axis of the mandrel thereby rolling said rolling means on a helical path relative to the periphery of the mandrel at a helix angle to progressively thin and spread the material of the circumferential wall of the receptacle to lengthen the circumferential wall to at least the desired axial dimension of the can body.

11. A method as set forth in claim 10 in which the rolling means is maintained at a constant spacing from the axis of the mandrel and in which the mandrel tapers at its opposite ends with the consequence that the thickness of the circumferential wall of the finished can body tapers from both ends towards the central region thereof.

References Cited OTHER REFERENCES Product Engineering, August 1956, Power Spinning Conical and Tubular Parts.

CHARLES W. LANHAM, Primary Examiner M. J. KE-ENAN, Assistant Examiner US. Cl. X.R. 7282, 126, 377 

